LeetCode: 1302. Deepest Leaves Sum

题目

原题地址：https://leetcode.com/problems/deepest-leaves-sum/

Given a binary tree, return the sum of values of its deepest leaves.

Example 1:

image

Input: root = [1,2,3,4,5,null,6,7,null,null,null,null,8]
Output: 15

Constraints:

  • The number of nodes in the tree is between 1 and 10^4.
  • The value of nodes is between 1 and 100.

解法

通过前序遍历寻找最深的节点，然后将他们的值相加，可以在寻找节点的过程中做相加操作。

这个方法的 Python 代码类似下面这样:

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def deepestLeavesSum(self, root: TreeNode) -> int:
        self._max_depth = 0
        self._sum = 0
        self._preorder(root, 0)

        return self._sum

    def _preorder(self, root, current_deepth):
        if root is None:
            return

        # 将最深的节点值详见
        if current_deepth == self._max_depth:
            self._sum += root.val

        # 发现更深的节点，更新 max_depth 信息同时重置 sum 的值
        if current_deepth > self._max_depth:
            self._max_depth = current_deepth
            self._sum = root.val

        self._preorder(root.left, current_deepth + 1)
        self._preorder(root.right, current_deepth + 1)

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